1. Field of the Invention
The present invention relates to intake and exhaust control systems for an engine, in which an intake control valve for changing an intake mode in accordance with an operational state of an engine is provided in an intake system of the engine, and an exhaust control valve for changing an exhaust mode in accordance with an operational state of the engine is provided in an exhaust system of the engine.
2. Background Art
A conventional intake control system operates an intake system for an engine and has an intake control valve operated between a first intake control position, at which it gives a low speed side compatible function to the intake system, and a second intake control position, at which it gives a high speed side compatible function to the intake system. Such a conventional system is disclosed in Japanese Patent Laid-open No. Sho 58-155270.
A conventional exhaust control system operates an exhaust system and has an exhaust control valve operated between a first exhaust control position, at which it gives a low speed side compatible function to the exhaust system, and a second exhaust control position, at which it gives a high speed side compatible function to the exhaust system. This type of conventional system is disclosed in Japanese Patent Publication No. Hei 6-76780.
If the above-described intake control valve and exhaust control valve are provided in an intake system and an exhaust system of the same engine, the output performance in a wide rotational range of the engine can be further improved. However, because the control valves are individually driven by separate actuators, the number of parts is increased, increasing cost.
A need therefore exists for an intake and an exhaust control system capable of improving the performance of the engine in both low and high speed rotational ranges.
The present invention overcomes the shortcomings of the conventional art and achieves other advantages not realized by the conventional art.
According to one embodiment of the present invention, intake and exhaust control systems for an engine are provided in which an intake control valve for changing an intake mode in accordance with an operational state of an engine is provided in an intake system of the engine, and an exhaust control valve for changing an exhaust mode in accordance with an operational state of the engine is provided in an exhaust system of the engine. The intake control valve and the exhaust control valve are driven by a common actuator.
According to this aspect of the invention, it is possible to obtain a desired output performance of the engine, irrespective of a change in the operational state of the engine, by operating the intake control valve and the exhaust control valve in accordance with the operational state of the engine. The intake valve and the exhaust control valve can be operated by the common actuator.
Further, since the intake control valve and the exhaust control valve are driven by the common actuator, it is possible to simplify the configuration of the drive system, and thereby improve the engine performance. The cost and weight of the drive system are also reduced.
According to a second aspect of the present invention, the intake control valve is operated between a first intake control position, at which the intake control valve gives a low speed side compatible function to the intake system, and a second intake control position, at which the intake control valve gives a high speed side compatible function to the intake system. The exhaust control valve is operated between a first exhaust control position, at which the exhaust control valve gives a low speed side compatible function to the exhaust system, and a second exhaust control position, at which the exhaust control valve gives a high speed side compatible function to the exhaust system.
The first exhaust control position and the second exhaust control position of the exhaust control valve are equivalent to a medium speed control position and a high speed control position of a valve body of an exhaust control valve.
According to the second aspect of the invention, since at the low speed rotational range of the engine, the intake control valve, and the exhaust control valve are held at the first intake control position and the first exhaust control position by the actuator, respectively, it is possible to give the low speed side compatible function to both the intake system and the exhaust system. This enhances the low speed side output performance of the engine.
When the rotational state of the engine is shifted to the high speed rotational range, since the intake control valve and the exhaust control valve are moved to the second intake control position and the second exhaust control position by the actuator, respectively, it is possible to give the high speed side compatible function to both the intake system and the exhaust system. This enhances the high speed side output performance of the engine.
According to a third aspect of the present invention, a lost motion mechanism for absorbing a difference in operational amount between the intake control valve and the exhaust control valve is provided between the actuator and the intake control valve, or between the actuator and the exhaust control valve. In the third aspect, even when there is a large difference between the operational amounts of the intake control valve and the exhaust control valve, such a difference can be absorbed by the lost motion mechanism, so that both the control valves can be certainly operated by the common actuator.
According to a fourth aspect of the present invention, the exhaust control valve may include a common valve housing interposed on the way of a first exhaust pipe, and a second exhaust pipe connected to cylinders having differing ignition timing. A valve body is mounted in the valve housing and switchably turned between a low speed control position, a medium speed control position, and a high speed control position. At the low speed control position of the valve body, the first exhaust pipe is communicated to the second exhaust pipe, and the first exhaust pipe is closed on the downstream side of the communicated portion. At the medium speed control position, the first exhaust pipe and the second exhaust pipe individually allow exhaust gases to pass therethrough. At the high speed control position, the first exhaust pipe and the second exhaust pipe individually allow exhaust gases to pass therethrough, and an intermediate portion of the first exhaust pipe is communicated to an intermediate portion of the second exhaust pipe.
According to the fourth aspect, exhaust gas flowing in the first exhaust pipe is curved, on the way, onto the second exhaust pipe side by controlling the valve body at the low speed control position, in order to increase the exhaust resistance. It is therefore possible to apply an exhaust pressure suitable for the low speed rotational range to the engine, and hence to improve the low speed output performance by suppressing the blow-by of a new air from each cylinder to the exhaust system during the valve overlapping period. The effective pipe length of each of the first and second exhaust pipes is set at the maximum length matched to the medium speed operational range of the engine by controlling the valve body at the medium speed control position. This enhances the volume efficiency by making use of an exhaust inertia effect and/or an exhaust pulsation effect, thereby increasing the medium speed output performance of the engine. Further, the effective pipe length of each of the first and second exhaust pipes is set at the minimum length matched to the high speed operational range of the engine by controlling the valve body at the high speed control position. This enhances the volume efficiency by making use of the exhaust inertia effect and/or the exhaust pulsation effect, thereby increasing the high speed output performance of the engine.
According to a fifth aspect of the present invention, the valve body is supported in the valve housing so as to be turned between the low speed control position, the medium speed control position, and the high speed control position. The valve body has a through-hole crossing the axial line of the valve body, and a communication hole for opening one side surface of the through-hole in the radial direction of the valve body. At the low speed control position of the valve body, the communication hole and the through-hole are concerned with the mutual communication of the first exhaust pipe and the second exhaust pipe, and a valve wall, opposed to the communication hole, of the valve body is concerned with the closing of the downstream side of the first exhaust pipe. At the medium control position, the through-hole is matched to the pipe line of the first exhaust pipe, and the valve wall is concerned with the blocking between the first exhaust pipe and the second exhaust pipe. At the high speed control position, the through-hole is matched to the pipe line of the first exhaust pipe, and the communication hole is concerned with the communication between the first exhaust pipe and the second exhaust pipe.
According to the fifth aspect, it is possible to equalize the cross-section of the pipe line of each exhaust pipe over the effective pipe length matched to each operational range of the engine irrespective of the presence of the valve body. Effective exhaust inertia effect and/or exhaust pulsation effect that is matched to each operational range may therefore be obtained. In particular, when the valve body is controlled at the medium speed control position, it is possible to equalize the cross-section of the pipe line of each exhaust pipe over the entire length, and hence to significantly obtain the above-described effect and improve the medium speed output performance of the engine.
According to a sixth aspect of the present invention, of the first exhaust pipe and the second exhaust pipe on the downstream side from the valve housing, only the second exhaust pipe is connected to a primary exhaust purifying system. The first exhaust pipe and the second exhaust pipe are connected to an exhaust collection pipe on the downstream side from the primary exhaust purifying system. A secondary exhaust purifying system is provided in the exhaust collection pipe.
According to the sixth aspect, in the low speed operational range of the engine, in which the flow rate of exhaust gas is relatively small, the valve body is controlled at the low speed control position. In this case, all of the exhaust gas having passed through the valve housing can be sequentially introduced to the primary and secondary purifying systems, thereby purifying the exhaust gas. The primary exhaust purifying system can be heated to an activation temperature at an early stage, and the entire cost of the exhaust purifying systems can be reduced because an exhaust purifying system is not provided on the first exhaust pipe side. In the medium or high speed operational range of the engine, the valve body is controlled at the medium or high speed control position. In this case, the exhaust gas having passed through the first exhaust pipe does not pass through the primary exhaust purifying system; however, in such a state, the flow rate of the exhaust gas becomes relatively large and all of the exhaust gas passes through the secondary exhaust purifying system. Therefore, the purifying function of the secondary exhaust purifying system is sufficiently enhanced by the exhaust heat of the exhaust gas, and the reaction heat, and thereby all the exhaust gas can be effectively purified.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.